Chronic pelvic pain associated with endometriosis is poorly understood. Some women with chronic pelvic pain have muscle spasm of their pelvic muscles. Muscle spasm may be a significant part of pain in women with endometriosis and other types of chronic pelvic pain. Botulinum toxin injection is widely used to treat conditions associated with excessive muscle activity and spasm. Studies of botulinum toxin injected into pelvic muscles of women with pelvic pain have shown a decrease pain and spasm, but too few women have been studied to conclude its effectiveness. We expect to show that botulinum toxin injection in women with pelvic pain will relieve some of their pelvic pain. Eligible subjects are otherwise healthy women who have chronic pelvic pain and a history of endometriosis. Subjects will be randomized to either botulinum toxin injection or placebo (salt water) injection. After one month, we will evaluate the presence of the pain and all women will be offered botulinum toxin injection. We will also evaluate the need for reinjection. The purpose of this study is to determine if botulinum toxin injections into the muscles of the pelvic floor can relieve chronic pelvic pain in women with pelvic muscle spasm. After a number of administrative delays, a CTA was implemented with Allergan, Inc., a study initiation visit was completed and enrollment began in July 2014. The study is now fully underway. In the year since enrollment started, we have made good progress with 9 enrolled participants, 3 women who have entered the pre-screening phase of the study, and another 4 who have expressed interest.